The invention pertains to a gas mixer comprising: a first, external gas housing part with a feed line for the first gas in a longitudinal axis and a feed line for the second gas in a transverse axis; a second, internal gas housing part, which is inserted into the first gas housing part to form an annular space for a second gas, with a mixing space, into which the first gas and the second gas can be introduced so that they can be mixed to form a gas mixture; wherein the first gas housing part, the second gas housing part, and the annular space are oriented along the longitudinal axis, while the mixing space is oriented cylindrically along the longitudinal axis; and wherein a mixing arrangement consisting of a number of hollow bars is arranged in the mixing space; wherein a hollow space of a hollow bar is fluidically connected at both ends to the annular space. The invention also pertains to a gas mixing system with a gas engine.
A gas mixer of the type described above serves to mix together a first gas and a second gas. Especially in the case of a gas engine, the first gas is in the form of combustion air, that is, fresh air or a lean air/gas mixture—also called “charge air”, and the second gas is in the form of a fuel gas. The gas mixer provides an air/fuel gas mixture, consisting of combustion air into which a fuel gas is mixed, suitable for the gas engine. Especially for a lean gas engine, it has been found important to adjust the lambda ratio, namely, the ratio of fuel gas to combustion air—to suit the power demand of the lean gas engine, for example. A gas mixer is described in EP 0 898 064 A1, for example, where it appears in the form of a venturi mixer, which is positioned in a gas mixing system upstream of a lean gas engine to add fuel gas to the combustion air or a lean gas mixture and to mix these two components together.
To increase the mixing quality of the air/fuel gas mixture, it is possible in principle to work with a venturi mixer with different cross sections; EP 2 258 983 A2, for example, describes a mixing section of a venturi mixer provided with different cross sections. GB 154,920 describes a gas mixer of the type previously mentioned with a movable displacement body in a venturi tube, as a result of which a mixing gap can be set to different values. A venturi mixer works on the basis of the venturi principle, on which the mixing of the gases depends; that is, what is essential is to reduce the overall backpressure in the flow by increasing the flow velocity in the area of a displacement body, this displacement body being arranged centrally in the flow to reduce the overall size of the flow cross section. This essential “global” venturi principle is thus based on the use of a central displacement body, which influences, i.e., accelerates, the flow over the entire flow cross section.
EP 2016 994 A describes a gas mixer of the type indicated above, in which a venturi tube comprises inlet openings for the fuel gas in the area of a narrowed cross section; the size of these openings can be varied by control elements during the mixing process. The control elements comprise here a control sleeve, which surrounds the narrowed cross section and has fuel control openings, wherein the size of the pass-through cross sections for the fuel gas can be changed by shifting the position of the fuel control openings with respect to the position of the inlet openings for the fuel gas. The narrowed cross section is formed by a displacement body arranged in the venturi tube. Although it is possible in this way achieve a comparatively precise adjustment of the pass-through cross section, it takes a comparatively long time to execute the corresponding control process, and the maximum allowable actuating force is also limited. In addition, the mechanical design of the previously mentioned control elements is comparatively complicated, which means that the precision with which adjustments can be made will deteriorate over the service life of the gas mixer as a result of wear and possibly the accumulation of dirt.
In addition to a displacement body, which is usually torpedo-shaped, all of the previously mentioned solutions are characterized by an increasingly narrow flow-through opening extending around the displacement body, which is arranged on the center axis. This leads to the maximum possible acceleration of the combustion air in the area of the narrowed flow-through opening and thus produces a high negative pressure across the entire cross section of the narrowed flow-through opening, sufficient to allow the admixture of the fuel gas. This mixing principle, called here the “global” venturi principle, makes use of the venturi effect across the entire cross section of the narrowed flow-through opening, thus making it the primary and essential principle of the mixing process.
The venturi principle generally offers the basic advantage that the quantities of fuel gas and combustion air remain at the same ratio to each other, even if, for the purpose of changing the power output, a throttle valve is adjusted to change the central mass rate-of-flow of the first gas, i.e., the air.
Theoretically, the venturi principle also works loss-free; that is, theoretically, it works without a loss of total pressure. In reality, however, it is found that, in the case of a venturi nozzle, a negative pressure gradient, that is, a pressure difference between the feed of the second gas and the feed of the first gas, attributable to the use of the “global venturi principle”, depends on the number of cylinders of the gas engine connected to the gas mixer or on the equivalent volume of the system making use of the gas. For example, it is to be observed that a gas engine with more than a double-digit number of cylinders can cause a total pressure loss at the gas mixer in the double-digit mbars range. A total pressure loss of this type must be compensated regularly by the compressor of an exhaust gas turbocharger, usually installed downstream from the gas mixer; this means that the power produced by the compressor changes with the variation of the total pressure loss, which impairs the overall efficiency of an internal combustion engine equipped with the gas mixer, especially a gas mixing system with a gas engine or the like. This proves to be especially disadvantageous when the second gas is a combustible gas such as natural gas, biogas, or similar type of fuel gas with a highly variable CO2 component and the first gas is charge air or similar type of combustion air.
It is desirable to design a gas mixer in such a way that the compressor of the internal combustion engine is relieved of this load. It is also desirable to have a gas mixer of comparatively simple design which offers a long and reliable service life.